1. Field of the Invention
The present invention relates to compositions and methods for forming films that are useful, for example, in controlling mastitis and healing wounds. More particularly, pullulan-based compositions form barrier films that are useful in protecting animals from microbial infections.
2. Description of the Related Art
One major cause of economic loss for dairy farmers is the incidence of mastitis in cows and other dairy animals. Mastitis is typically caused by infection of the milk ducts by microorganisms. Severe cases of mastitis may cause death, while milder cases may result in loss of milk production together with an increased cost of veterinary care. Annual economic losses due to mastitis approximate $185 per dairy animal, which totals to approximately $1.7 billion annually for the entire United States market.
Dairy farmers have traditionally taken two approaches to prevent cows from contracting mastitis. One measure employs germicidal agents that kill microbes. The other approach uses a persistent film-forming composition that is applied to bovine teats as a barrier to block microbes from entering the milk ducts.
Despite intensive research and testing of compositions that can effectively protect animals from mastitis, many problems persist. For example, although many compositions are capable of forming a layer of film over the teat skin, some films tends to crack during drying, leaving some areas of teat skin unprotected. Other compositions form a layer of film over the skin that is too easily washed off when in contact with manure, mud or water. Still other materials cannot be removed easily enough, and may be a source of contamination that complicates the milking and milk purification processes. Moreover, some film-forming components are incompatible with germicides and other chemical ingredients that may be found in teat dip formulations, resulting in reduced potency of the germicide(s). It is difficult to formulate a protective film that is continuous, uniform, non-brittle, and persistent for 8-12 hours between milking, and mild on skin, easily removed by cleaning prior to milking, and does not drip when applied.
One type of barrier utilizes cellulose as a barrier-forming agent. For example, U.S. Pat. No. 5,776,479 issued to Pallos et al. discloses a germicidal teat dip composition that contains a film-forming ingredient selected from hydroxyethyl cellulose, methylhydroxypropyl cellulose and ethylhydroxyethyl cellulose. The composition includes a germicidal agent, such as iodine, which complexes with a nonionic surfactant and water to provide a solution having a viscosity of from about 50 to 1000 cP. After being applied to the teats of agricultural animals, the liquid dries to form a continuous barrier film.
EP 896,521 B1 describes a barrier-forming mixture that uses a long chain polysaccharide derivative, such as methyl cellulose or hydroxyethyl cellulose, which is present in an amount ranging from 10% to 20% of the composition by weight. The efficacy of this polysaccharide material is enhanced by the use of a low molecular weight saccharide material that may be, for example, a monosaccharide or disaccharide and may include hydrolyzed starches, such as maltodextrin. Although the polysaccharide material and the saccharide material are not exceptionally effective alone, a synergistic effect is achieved when the materials are used in combination such that the low molecular weight saccharide is present in an amount ranging from 2% to 10% of the composition by weight.
The use of polysaccharide-based cellulose and cellulose derivatives in teat dip compositions presents a number of problems. For example, the solutions tend to drip after application resulting in a certain amount of wasted product. Dripping of the applied solutions also results in a thinner barrier film than is ideal for use on the animals. Further, it is difficult to formulate quick-drying compositions because cellulose is relatively insoluble in commonly used volatile solvents, such as short chain alcohols.